Certain printers and imaging devices and machines require the use of a belt in the printing or imaging region of the device or machine. Depending on the particular application, the belt may be used to perform any one of several functions. For example, the belt can be used to perform a printer transport function, i.e., to transport and hold paper (or another material to be printed on) in the printing area of a conventional printer. The belt carries paper or the like and positions the same in front of the print head and, after printing, the belt indexes, thereby feeding the printed paper to the next area or section of the machine. The transport and holding function is usually assisted by a vacuum, drawn through perforations in the belt. Endless belts are also used as imaging belts, wherein the belt is charged with an image, the charge on the belt receives a toner and the image is then transferred to paper or another suitable material.
There are a number of important requirements to be met before a belt can be used in such applications. These requirements include, among others, the following: (1) the belt must be seamless or have a minimal or undiscernible seam; (2) the belt must be electrically conductive; (3) the belt must have good temperature resistance characteristics (as is discussed in more detail below); (4) the belt must be flexible; (5) the belt must have customized (controllable) frictional characteristics; (5) the belt must be thin (both for greater flexibility and for heat transfer advantages, as discussed below); and (6) the belt must be resistant to creasing.
There are, of course, a number of belts that are candidates for use in the applications described above but no single prior art belt embodies all of the advantages and meets all of the requirements set forth above. Two principal types of prior art belts are coated, woven endless belting and ultrasonically welded, thermoplastic film belts. The former, i.e., coated, woven, endless belts, possess many of the characteristics discussed above but that technology is not presently capable of providing very thin belts, i.e., belts having a thickness equal to or less than about 0.010 inches. Regarding the second type, although welded plastic (e.g., polyester (Mylar)) film belts have been employed in some applications, there are several problems and disadvantages with such belts in other important applications. For example, because of the thickness increase ("bump") at the weld, the seam shows up when printing on paper over the seam area. Further, when imaging directly onto the belt, i.e., in an application where the belt is used as an imaging belt, the seam also shows up on the paper and the image thereof is transferred. In addition, plastic film belts are easily creased, thus creating handling problems. Further, plastic film materials which are amenable to welding generally do not have the inherent temperature capabilities required. (Again, these requirements in connection with the specific application mentioned previously are discussed in more detail below.) A further disadvantage of plastic film belts is that surface conductivity is not easily achieved and bulk conductivity does not exist in materials meeting the temperature constraints in question. Also, plastic film belts are not very flexible and this is a disadvantage for a number of reasons. For example, where a vacuum assist is used, the vacuum is not as effective. Further, flex life is diminished. A further disadvantage is that plastic film belts are not readily coated, in an endless fashion, with elastomeric materials (such as may be required to render the belts conductive). In this regard, such belts cannot be coated prior to welding in that the coating will greatly inhibit the welding process.
Patents of interest in the field of belts include the following: U.S. Pat. Nos. 4,823,942 (Martin et al); 3,542,633 (Goldsmith); and 3,482,676 (Fackler). The Martin et al patent relates to a document transport belt having a light reflective outer layer and an electrically conductive inner layer. The outer layer is made of ethylene propylene rubber or ethylene propylene diene rubber containing light reflective pigments. The electrically conductive inner layer is made of ethylene/propylene rubber or ethylene/propylene diene rubber containing conductive carbon black. The outer layer and inner layer are joined together to form a plied sheet. Heat and pressure are applied to the plied sheet to cure the base polymer in both layers. The Goldsmith patent relates to an electrically conductive anti-stick conveyor belt. The foraminous substrate of the belt is preferably made of glass fiber cloth, but may be made of other flexible materials. The substrate is provided with openings, either inherently through its weave or directly formed with openings by perforating. The flexible substrate is coated with a fluorocarbon polymer to provide anti-stick properties. This base coating, which is non-conductive, is, in turn, covered with a conductive fluorocarbon coating so that electrostatic charges on the face of the belt can leak off through the conductive coating to the back of the belt to grounded backing plates or rollers. The Fackler patent relates to a belt for a document feeding apparatus having a light reflective outer layer and an electrically conductive inner layer. In a typical example, the outer belt layer is made of a white or light colored polyolefin or neoprene and the inner layer is made of graphite impregnated neoprene. The layers are secured together by bonding.
Other patents of possible interest include the following: U.S. Pat. Nos. 4,526,357 (Kuehnle et al); 4,287,984 (Okamoto et al); 4,244,465 (Hishikawa et al); 3,986,773 (Marx et al); 3,584,733 (Isermann); 3,437,336 (Enke et al); and 2,576,882 (Koole et al).